1. Field of the Invention
This invention relates generally to a rack for mounting and connecting a plurality of electronics modules and, more particularly, to a rack for mounting and connecting a plurality of electronics modules, where the rack does not include inlet and outlet cooling plenums.
2. Discussion of the Related Art
Many electronic systems employ independent electronics modules that are slidably positioned within an electronics rack, and electrically connected to each other therein. One particular known electronics rack is used for mounting and connecting avionics electronics modules. As is well understood in the art, the operation of electronics systems generates heat. The closer the electronics modules are mounted together, the more heat is generated per unit area, and the harder it is for the heat to dissipate. If too much heat is generated, the electronics modules may not operate correctly, and their useful life will be reduced. Additionally, generation of a significant amount of heat creates a fire hazard. Therefore, one of the primary functions of the rack is to provide cooling of the modules.
In one rack design, cooling air is forced through a heat exchanger configured within the rack to provide cooling of the electronic modules. FIG. 1 is a perspective view of an electronics rack 10 of this type that is known in the art. The rack 10 includes an outer housing 12 having a front opening 14. A lower card guide 16 is mounted at a lower location within the housing 12 by flanges 18 secured to opposing side panels 20 and 22 of the housing 12. The card guide 16 is a single piece unit made of a heat conductive metal, such as aluminum. The card guide 16 includes a plurality of parallel tabs 28 extending from front to back that define grooves 30 therebetween. Each tab 28 includes an alignment nub 32 positioned proximate the opening 14. An upper card guide (not shown) is also mounted within the housing 12 at an upper location in the same manner, and also includes parallel tabs defining grooves therebetween.
The parallel grooves 30 in the lower card guide 16 and the parallel grooves in the upper card guide are aligned and suitably spaced apart to receive electronics modules 36 in a certain configuration. Each electronics module 36 includes a lower tab 38 that is inserted in one of the grooves 30 in the lower guide 16 and an upper tab 40 that is inserted in a corresponding groove in the upper guide. When the module 36 is slid into the housing 12, an electrical connector 42 is electrically connected with a mating electrical connector (not shown) at the back of the housing 12 to provide the desired electrical connection. Multiple electronics modules 36 are slid into the housing 12 in a parallel format to provide the overall electrical system. It is generally desirable to set the spacing of the grooves 30 and the thicknesses of the electronics modules 36 to allow as many modules 36 as possible to be stored in the rack 10 to conserve space.
The modules 36 generate heat during operation. The rack 10 therefore provides assisted cooling of the modules 36 to draw away the heat. FIG. 2 is a cross-sectional view of the rack 10 through line 2--2 in FIG. 1. The tabs 38 and 40 make contact with the lower card guide 16 and the upper card guide in a heat transfer engagement. To provide the cooling, forced air is caused to circulate across the lower card guide 16 and the upper card guide to draw heat away from the modules 36. An inlet plenum 46 is attached to the side surface 20 at one side of the housing 12 and an outlet plenum 48 is attached to the side surface 22 at an opposite side of the housing 12. Of course, the inlet and outlet plenums 46 and 48 can be reversed. The inlet plenum 46 includes a rectangular opening 50 through a backwall 52 of the housing 12 that allows cooling air to enter the plenum 46. The outlet plenum 48 includes a rectangular opening 54 through the wall 52 that allows the heated air to exit the outlet plenum 48 and the housing 12.
A heat exchanger 60 is positioned within a specially configured cavity in a base plate 62 between a bottom wall of the housing 12 and the card guide 16. A similar heat exchanger is also provided between the top wall and the upper card guide. The heat exchanger 60 includes a plurality of spaced apart fins 64 that extend transverse to the opening 14. The cooling air from the inlet plenum 46 is forced into the heat exchanger 60 and flows between the fins 64 across the card guide 16 to collect heat therein. The fins 64 increase the surface area exposed to the cooling air to increase the heat removal capacity. As the operation of the modules 36 heats the upper and lower card guides, air flowing between the fins 64 acts to draw heat away from the modules 36, providing the cooling. The inlet plenum 46 provides cooling air to both the upper and lower heat exchangers.
The spacing between the cooling fins 64, and the height and width of the cooling fins 64, is determined by the desired amount of air flow to provide the desired amount of cooling, as is understood in the art. In alternate varations, the rack 10 can include a plurality of stack layers where electronics modules 36 are positioned between card guides in each separate layer, and cooling is provided at each layer in the manner as discussed herein.
The above-described process of providing cooling of electronics module in an electronics rack has been effective in removing heat from the electronics module. However, the overall electronics packaging density of the system is reduced because finite amounts of volume must be dedicated to the inlet and outlet plenums 46 and 48. Because the size and weight of the electronic system may be an important parameter in different types of systems, it may be desirable to provide an electronics rack that eliminates the plenums 46 and 48, but distributes cooling air to the modules 36 at a higher or at least as high volumetric efficiency. It is therefore an object of the present invention to provide such a plenumless electronics rack.